1. Field of the Invention
The present invention relates to a thermal assisted magnetic recording head with a plasmon generator.
2. Description of the Related Art
In recent years, in magnetic recording devices typified by magnetic disc devices, there has been a need for performance improvement of a thin-film magnetic head and a magnetic recording medium in association with higher recording density. As a thin-film magnetic head, a composite type thin-film magnetic head is widely used in which a reproducing head having a magnetoresistive effect element for reading, and a recording head having an induction type electromagnetic transducer element for writing, are layered on a substrate.
A magnetic recording medium is a discontinuous medium in which magnetic grains are aggregated, where each magnetic grain has a single magnetic domain structure. Each recording bit on a magnetic recording medium is configured with a plurality of magnetic grains. In order to enhance the recording density, the unevenness of the boundaries between adjacent recording bits must be smaller, and the magnetic grains must be reduced in size for this purpose. However, smaller magnetic grains, namely magnetic grains with smaller volumes, cause a reduction in thermal stability of magnetization. In order to solve this problem, it is effective to increase anisotropic energy of magnetic grains. However, high anisotropic energy of magnetic grains increases the magnetic coercive force of a magnetic recording medium and makes it difficult to record information with an existing magnetic head.
As a method of solving this problem, so-called thermal assisted magnetic recording is proposed. In this method, a magnetic recording medium with greater coercive force can be used. When information is recorded, a magnetic field and heat are simultaneously applied to a portion of the magnetic recording medium where information is recorded, and temperature of the portion is increased. Information is recorded to the portion where the magnetic coercive force has been decreased with this process by the magnetic field. Hereafter, the magnetic head used in thermal assisted magnetic recording is referred to as a thermal assisted magnetic recording head (TAMR head).
A typical TAMR includes a core that propagates light irradiated from a laser diode and a plasmon generator that generates near-field light. The plasmon generator is coupled with portion of the propagated light propagates in the core in the surface plasmon mode and generates a surface plasmon, propagates the surface plasmon up to the end surface situated on the air bearing surface, and generates near-field light at the end surface.
In the existing TAMR head, deterioration of recording properties (the S/N ratio and the like) associated with continuous recording is confirmed. Deformation of the plasmon generator, particularly recession of the end surface of the plasmon generator from the air bearing surface facing the magnetic recording medium, has been recognized as the main factor. For example, deformation due to agglomeration at the end surface of the plasmon generator is an issue. The agglomeration is a phenomenon of metal atoms gathering, which results from diffusion and migration of metal atoms due to heat and stress as driving force. The air bearing surface of a magnetic head slider and the surface of a magnetic recording medium are asperous, and the end surface of the plasmon generator sometimes makes contact with the magnetic recording medium while the magnetic recording device is in operation. Raised temperature and increased stress due to the impact causes the agglomeration. The agglomeration is likely to cause the end surface of the plasmon generator to recess from the air bearing surface. Consequently, the distance between the plasmon generator and the magnetic recording medium is increased, and the ability of heating the magnetic recording medium deteriorates with time, causing deterioration in the S/N ratio and the like. Therefore, it is desired to suppress the agglomeration in the plasmon generator in order to ensure the reliability of a TAMR head.
The agglomeration tends to occur to a plasmon generator consisting of gold (Au), which is suitable to generate near-field light, and to occur particularly in the vicinity of the air bearing surface where the volume is small (the part of the plasmon generator that is tapered toward the air bearing surface). In order to suppress the agglomeration, it has been proposed to add 0.2 at % to 2.0 at % of elements such as copper (Cu) and Iron (Fe) to Au to create an alloy and thus improve hardness (U.S. Pat. No. 8,964,514). However, alloys such as AuCu and AuFe are poor in efficiency of surface plasmon propagation, and significant plasmon propagation loss occurs and causes heat generation in the plasmon propagation region of the plasmon generator. Consequently, reliability is decreased. Therefore, although it is effective to suppress the recession (recess) of the end surface of the plasmon generator from the air baring surface, heat generation due to plasmon propagation loss increases.
U.S. Pat. No. 7,529,158, U.S. Pat. No. 8,305,849, and U.S. Pat. No. 8,576,674 disclose techniques for improving the reliability of a thermal assisted magnetic recording head by forming a part of the end of the plasmon generator with a highly heat-resistant material (for example, Pt, Pd, Rh, and Ir), not with Au. However, when the material of the end of a plasmon generator is replaced with Pt, Pd, Rd, Ir, or the like rather than Au, the capability of confining the near-field light decreases, and it is difficult to realize high density recording.
As described above, it is difficult to achieve both improvement in the heat resistance and the mechanical strength of a plasmon generator itself and improvement in the recording performance (for example, recording density) because these variables have a trade-off relationship. Therefore, it is desired in a plasmon generator consisting mainly of Au for improving the recording performance to identify and reduce the factors accelerating the deformation. One of the factors accelerating the deformation of a plasmon generator consisting mainly of Au is, as described above, agglomeration associated with heat generation of the plasmon generator itself, and some countermeasures have been attempted. However, there are limitations on taking countermeasures for heat generation of a plasmon generator while suppressing reduction in the recording performance such as recording density, and the deformation is not sufficiently suppressed in some cases. On the other hand, factors other than heat generation accelerating the deformation of a plasmon generator have not been studied in detail, and thus no particular countermeasure has been taken.
The objective of the present invention is to provide a thermal assisted magnetic recording head capable of suppressing the deformation of the plasmon generation while maintaining the configuration for improving recording performance.